A novel structure for coalescing the droplets and producing the droplets’ array in silicone oil

Abstract

In this paper, a strategy for coalescing the droplets and producing the droplets’ array based on non-contact manipulating individual droplets in silicone oil and through acoustic streaming is demonstrated. A trapezoidal fattened tip of vibrating needle, which is driven by a sandwich-type transducer in 42 kHz, is used to generate spiral vortex fields in silicone oil to non-contact manipulate individual droplets. The patterns of the spiral vortex fields were measured by experiments and calculated by FEM, separately. After validating the FEM model, the distributions of the fluid’s velocity in x direction were calculated. Then, to avoid the droplet being captured on the manipulator’s tip, the intervals of the distance between the manipulator’s tip and droplets for non-contact manipulating the droplets were determined by investigating the relationship between the maximum (and minimum) value of such distance and the volume of the manipulated droplets. In addition, to avoid disturbing the other droplets during re-ordering the individual droplet’s position, after transforming the above intervals to the intervals of inserting depth of the manipulator’s tip, the relationship between the inserting depth and the maximum influencing distance to the droplets was also investigated. In the experiments, two droplets were coalesced to a new one. In addition, four and nine droplets were patterned “7” and a 3*3 matrix, separately. Due to the ability of re-ordering micro-liter droplets’ position without emulsification, it proves that this method is suitable used in analyst chemistry, biomedicine, biology fields and etc.